1. Field of the Invention
The invention disclosed in this specification relates to a method of manufacturing an integrated thin film semiconductor device. The invention disclosed in this specification also relates to a method of manufacturing an active matrix type liquid crystal display.
2. Background of the Invention
Active matrix type liquid crystal displays have been conventionally known. They have a configuration wherein a thin film transistor is provided at each of pixel electrodes provided on a glass substrate in a quantity on the order of several hundred thousands. The thin film transistor provided at each pixel electrode has a function of controlling charge going in and out the pixel electrode.
Another configuration is known in which a thin film transistor circuit (referred to as "driver circuit") for driving the thin film transistors provided at the pixel electrodes is integrated on the same glass substrate. This is referred to as "peripheral-integrated active matrix type".
During the manufacture of such an active matrix type liquid crystal display, a phenomenon is encountered in which some of the thin film transistors integrated on the glass substrate malfunction.
The inventors have actively studied this problem and reached the findings described below.
When an integrated semiconductor device such as an active matrix type liquid crystal display is manufactured, the formation of insulation films and wiring is performed using the plasma CVD method or sputtering method and plasma etching.
FIG. 3 schematically illustrates the relationship between the energy (relative value) and quantity (relative value) of ions during generation of plasma. In general, there are relatively not a few high energy ions which give plasma damage to the substrate as indicated by the oblique lines in FIG. 3.
Meanwhile, there is a fact that an insulation film formed using plasma CVD or sputtering is not fine and has a withstand voltage as low as about several tens volts or less. Further, there is a problem that the used substrate is very easily charged because the substrate is made of glass or quartz which is a substantially complete insulator.
FIG. 4(B) illustrates one step of the manufacture of a thin film transistor as illustrated using symbols in FIG. 4(A). FIG. 4(B) shows a state of the formation of a interlayer insulation film 31.
In this case, it is assumed that the interlayer insulation film 31 is formed using plasma CVD or sputtering. It goes without saying that ions having high energy as shown in FIG. 3 collide with the sample during the formation of the film.
In general, a source (S) electrode and a gate (G) electrode are not connected to each other. Therefore, a situation may arise, although only locally, in which a potential difference between the source (S) electrode and the gate (G) electrode instantaneously reaches a value in the range from several tens volts to several hundred volts during a step using a plasma.
The source and gate electrodes are provided with an active layer 32 and a gate insulation film 30 interposed therebetween. The withstand voltage of the gate insulation film 30 formed using CVD or sputtering is several tens volts or less. Therefore, in the above-described situation, the gate insulation film 30 is electrically destroyed.
This causes the thin film transistor to malfunction. This problem can be solved by electrically shorting the source and gate electrode, that is, they have the same electrical potential during the formation of the interlayer insulation film 31. In a state in which the device is finally operated, however, the source and gate electrodes must not be directly electrically shorted.
Taking this into consideration, in the process shown in FIG. 4(B). the source and gate electrodes must be electrically shorted until the final stage, and then, they must be disconnected.